Dual air chambered shock strut



United States Patent [72] Inventor Curtis W. Foster North Hollywood,California [21] Appl. No. 681,206 [22] Filed Nov. 7, 1967 [45] PatentedNov.l7, 1970 [73] Assignee Lockheed Aircraft Corporation Burbank,California [54] DUAL AIR CHAMBERED SHOCK STRUT 4 Claims, 4 Drawing Figs.

[52] US. Cl 244/104, 188/100; 267/65 [51] lnt.Cl B64c 25/58 [50] Fieldof Search 244/104; 188/100; 267/64, 65

[56] References Cited UNITED STATES PATENTS 2,892,626 6/1959 Scott et a1244/104X fll -v 1 3,304,076 2/1967 Doversberger 267/64 3,304,077 2/1967Eaton et a] 267/64 2,296,017 9/1942 Bound et al.. 244/104 2,519,5228/1950 Wells 244/104 3,393,883 7/1968 Smithet a1 244/104X FOREIGNPATENTS 819,164 7/1937 France .r 244/104 954,078 6/1949 France l.244/104 1,012,604 12/1965 Great Britain 244/104 Primary Examiner-MiltonBuchler Assistant Examiner-Paul E. Sauberer Attorney-George C. SullivanABSTRACT: A dual air chambered shock strut for aircraft,

having telescoping members which cooperate to define dual Patented Nov.17; 1970 Sheet 1 of 2 QFIG-2 IO STRUT EX TENSION INCHES IOO INVENTOR.

CURTIS W. FOSTER Agent Patented Nov. 17, 1970 sounce MANIFOLD s oPRESSURE Sheet FIG 4 INVENTOR; CURTIS W. FOSTER DUAL AIR CHAMBERED SHOCKSTRUT BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART ofthe strut from its fully extended position, for soft landings,

and good riding characteristics during takeoff with a full load of fuelin the aircraft. The problems ofsuch a compromise are especially acutein aircraft having a high takeoff-to-landing weight ratio.

The shock strut most commonly used incorporates a single 4 air-oilchamber having a single gas pressure. As a consequence, if theairchamber is under a gas pressure which is sufficiently high to withstandthe aircraft loads during takeoff, the air chamber is too hard to afforda soft landing, since the breakaway force is very high. Conversely, ifthe air chamber is under a low. gas pressure, the shock strut has goodlanding qualities because of the low breakaway force requirements butpoor taxiing characteristics because under such conditions the shockstrut is very rigid and nonresponsive to the aircraft load.

Another shock strut commonly used is the liquid spring device. The maindisadvantage with such a device is that it has linear spring load-strokecharacteristics, as contracted with in a vertical position and having aclosed end 11 adapted for connection to an-airc raft structure by meansof a lug 12 fixed to the closed end 1 l'. A pair oflugs l3 and 14 areintegral with I and extend oppositely outward from approximately midwayof the cylinder as additional means used to connect the cylinder 10 tothe aircraft structure.

Coaxially extending into the open end ofthe cylinder 10 is a piston orstrut means 20. This strut is adapted for attachment to an aircraftwheel through a fork and axle system attached to and extending generallydownward from the strut 20. A pair of links 22 and 23 which arepivotally connected to one another at pointA, connect the strut to thecylinder 10 through a pair of lugs 22a and 23a, respectively, and areused as one means to limit the extension of the strut 20. They alsoabsorb any torque loads transferred from the strut 20 to the cylinder10. Connected to the upper end of the strut 20 is a piston head 24. Aretaining ring 25 is also fixedly mounted to the upper end of the strut20. The bottom end of the cylinder 10 also has aretaining ring 15attached thereto. An annular spacer 16 is .mounted on the retaining ring15. with the upper portion of the sleeve 16 adapted for engagement withthe retaining ring 25 to the standard air-oil type strut which has morepreferable hyperbolic spring load-stroke characteristics. To compensatefor this, some liquid spring devices utilize dual liquid pressurechambers in order'to approximately simulate the hyperbolicspringload-stroke characteristics of the standard single air-oil chamber typestrut. However, all of the disadvantages of the standard air-oil 'typestrut discussed above also pertain to the dual chambered liquid springdevice, since both types approximate each other.

SUMMARY OF THE INVENTION Another object of the invention is toprovide'soft landings of limit the bottommost extension of the strut 20.

A shock strut pressure chamber, generally indicated at 30, includes afixed lower end member 31 with an orifice 32 defined therein. The'upperend of the chamber 30 is integrally connected to an end member 33.Axially movable within the cylinder 10 between end members 31 and 33 isa floating piston 35wliich separates the pressure chamber 30 into anupper chamber 36 and a lower chamber 37. The lower chamber 37communicates with a low pressure gas source by means ofa' conventionalinlet connector 38 while the upper chamber 36 is placed in communicationwith a relatively higherpressure gas source through an inlet tube 39extending from an extremity of the end member 33 and leading through thecylinder end 11. The tube 39 is appropriately retained in anonmovable-position with respect to the end 11. An oil reservoir 40 isdefined between the piston head 24 and the end member in the cylinder 10and is placed in communication with the chamber 37 through the presenceof the orifice 32. The floating" piston 35 is of dome-shapedconfiguration, having a pluralityof orifices 51 which are providedforintroduc tion ofgas from the pressure source 38 to pressure: chamber theaircraft by reducing the breakaway force of the landing gear.

Another object of the invention is to improve the aircraft ride whentaxiing over bumps or holes in the runway.

Another object of this invention is to provide a shock strut that has along shocking stroke and at the same time has a low fully extendedpressure.

Various other objects and advantages will appear frorn the followingdescription ofonc embodiment ofthe invention.

BRIEFDESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE INVENTION In theembodiment ofthe invention illustrated in FIG. 1, the device includes ahollow cylinder 10 adaptable for operation -37 when the piston 35 isabutted against the shoulders of the end member3l The piston 35 alsocooperates with the cylinder 10 to define an annular chamber52therebetween which also communicates via orifices 51 with the pressurechamber 37 thereby equalizing the pressure acting on the pistonsidewall. This permits the piston 35 to slide freely within cylinder 10with a high degree of stability.

ln operation", during the normal shocking stroke, the strut 20reciprocateswithin the cylinder 10 and is supported by the retainingring 15 at the lower end of cylinder 10;and by the retaining ring 25bearing against the interior of the cylinder 10. The annular spacer l6maintains the rings 15 and 25 in a spaced relationship to afford a morestable support to resist any bending ofthe gear. The strut 20 initiallymoves upward forcing the oil located above the piston head 24 throughthe orifice 32, thereby dissipating the primary portion of the impactenergy ofthe shocking stroke. Theremaining portion of the impact energyis available to compress the air in chambers 36 and 37. v

As stated above, the lower chamber 37 is maintained at a lower airpressure than is the upper air chamber 36. Therefore, under a normalshocking stroke, the floating piston 35 remains abutted against theshouldersfof the end member 31, while the piston head 24 compresses .theair in the lower chamber 37. However, if a higher reaction force isnecessary, the pressure in the lower chamber 37 forces the floatingpiston 35 to break away from the shoulders ofthe end member-3l tofurther compress the air in the upper chamber 36.

During takeoff, when the aircraft is at full weight, to counteract sucha load the air in both chambers 36 and 37 iscompressed by the strut 20and piston 35 to the degree necessary to balance the reaction force ofthe strut with the load of the .aircraft. If during the takeoff taxiingthe wheel hits a bump in the runway, the pressure chambers arecompressed further with the strut absorbing the shock of the load.

Preliminary to landing, the strut is of course in its fully extendedposition. Upon touchdown the strut breaks away and immediately begins toretract, since the only initial force opposing the strut is the pressureforce in the low pressure chamber 37. This low breakaway force insures asoft landing. Even though the aircraft may have a very hard touchdown,the high pressure chamber 36 takes up any of the excess load on the lowpressure chamber 37. After touchdown and during the taxiing, the strutremains responsive to any runwaybumps because the low pressure chamber37 is able to absorb the shock load.

Therefore, as can be seen, the amount of shock occurring during takeoffor landing and ultimately transferred to the aircraft fuselage isthereby greatly reduces.

FIG. 2 shows the pressure curve of the dual chamber shock strutrepresented by solid lines A and B. The curve is plotted by percent offully compressed pressure against the strut extension in inches. As canbe seen by the graph, the total stroke of the embodied strut is shown as20 inches, for illustrative purposes only. Line A represents that partof the curve where both the high and low pressure air chambers are beingcompressed. This normally occurs during takeoff when the aircraft has afull load of fuel and is at its heaviest, and at which time the strut isextended only a short distance. Line B represents that part of the curvewherein only the lower air chamber 37 is being compressed. This normallyoccurs during landing, at

which time the strut is in its fully extended position. Point Erepresents the breakaway force needed to initiate strut retractionuponlanding. it is again noted that this breakaway force is relativelysmall and provides for an unusually soft landing. When the aircraftmakes a relatively hard touchdown, both chambers are compressed and thestrut retracts to a point on line A where both chambers are compressed.

The advantages of this invention over the prior art can readily be seen.For example, were a single gas chambered strut placed under the samepressure as chamber 37, its pressure curve would be a hyperbolic curverepresented by line B and broken line C. As can be seen, the strut wouldhave good landing qualities with the low breakaway point; however, lineC. which represents the strut during takeoff, is nearly vertical.Therefore, during takeoff, a strut so constructed would be very rigidand nonresponsive to the changes in chamber pressure and poor takeoffand taxiing characteristic. would be undesirable for either passenger orcargo service.

ln contradistinction, if a single gas chamber strut were under a veryhigh pressure, for example the combined pressures of chambers 36 and 37,its pressure curve would be a hyperbolic curve represented by line A andbroken line D. Here the strut would have good takeoff qualities;however, its landing characteristics, as represented by line D, would bepoor. First of all, the breakaway force as represented by point P wouldbe relatively high, resulting in hard landing characteristics,.thisdespite the fact that the aircraft alighted softly. Secondly, uponlanding, the taxiing characteristics would be undesirably rough becauseof the flatness of curve D.

Therefore, it can be seen that the landing gear of this inventionutilizes the best parts of both curves to provide good strutcharacteristics throughout takeoff, landing and taxiing operations. i

FIG. 3 shows amodification of the pressure chamber 30, including theaddition ofa fixed sleeve 50 which abuts the lower end member 31 andintegrally forms the upper end member 33. The sleeve 50 consists of thesame material as the piston 35, while the cylinder is usually made of anunlike and stronger material, since the stresses on the cylinder 10 aregreater. The advantage of having the piston and cylinder being madeofthc same material is that the wear on both members is even and unduescoring is thereby prevented.

Finally, PK]. 4 shows a schematic diagram of an aircraft land gearsystem wherein three or more landing gears in accordance with theinvention are manifolded together to equalize the pressure in each ofthe gears'upper air chambers. This is particularly advantageous undercircumstances wherein the aircraft encounters runways or taxi stripshaving crowned pavements. Under such conditions the struts are sometimesrequired to be extended at different lengths. If the gearspressurechambers were not manifolded, unequal reaction forces would be developedin the different gears. However, because ofthe manifolded gas pressure,the reaction forces ofthe gears are equal whereby the aircraft loads areevenly distributed to each of the gears.

The landing gear system includes a plurality of gears 10, each gear incommunication with a manifold 60 through a line 6]. The manifold 60, inturn, is in communication to a gas pressure source 63 via line 65.

It will be understood that various changes in the details,

' materials, steps and arrangements of parts, which have been hereindescribed and illustrated in order to explain the nature oftheinvention, may be made by those skilled in the art within the principleand scope of the invention.

lclaim:

1. A dual air chambered shock strut assembly for an aircraft comprisingin combination: I

a vertical hollow cylinder having a closed upper end and an open lowerend, the closed upper end adapted to be connected to the aircraftstructure;

'a first piston having a working end extending into and reciprocablysealing the lower open end of the cylinder and being axially movabletherein, the other end of the piston adapted to be connected to anaircraft wheel;

a floating piston located in the cylinder and axially movable thereinand separating the cylinder interior into an upper gas-containingpressure chamber and a lower gas-and-oil containing pressure chamber;and

a fixed member having a restrictive orifice therein secured to saidcylinder intermediate the lower gas-andoil containing pressure chamber,whereby oil is forced through said restrictive orifice upon the shockingstroke of the assembly to dissipate impact energy. i

2. A landing gear assembly comprising in combination:

first and second telescoping members cooperating to define a cavitytherebetween;

pressure responsive means in one of the members reciprocably separatingthe cavity into a lower pressure chamber containing liquid and gaseousmaterials and an upper pressure chamber containing only a gaseousmaterial; and

a fixed member having a restrictive orifice therein secured to said oneof the members intermediate said lower pressure chamber, whereby theliquid material is forced through said restrictive orifice into theportion of the lower ,pressure chamber bounded by said pressureresponsive means and fixed member to dissipate impact energy of theshocking stroke.

3. A dual gas-chambered shock strut assembly for an aircraft comprisingin combination: an elongated hollow cylinder having an open an elongatedhollow cylinder having an open end and a closed end;

strut means slidably disposed at said open end of said cylinder andincluding a slidable piston head;

a fixed member including a restricting orifice mounted in said cylinder;

an oil and-gas containing chamber disposed in said cylinder and formedbetween said piston head and fixed member;

a floating piston slidably disposed in said cylinder, said floatingpiston disposed between said fixed member and closed end of saidcylinder;

an upper gas chamber disposed between said closed end and floatingpiston;

a lower. gaschamber disposed between said fixed member the oil flowingthrough said restricting orifice intothe lower and floating piston; gaschamber upon an impact stroke to absorb energy the lower gas chamber ata pressure less than the pressure in generated-in the lower gas chamber.

4. The assembly of claim 3 including a liner mounted in said 5 cylinderabout said fixed member, said floating piston being ,clidably disposedin said liner. v

the upper gas chamber;

said dil-and-gas and lower gas chambers directly communicating with eachother through said restricting orifice; and t

